This invention relates generally to an osteotomy technique, and more particularly to a method for performing a femoral osteotomy. A preferred manner of practicing the invention is described in conjunction with veterinary surgery on the leg of a dog.
Hip dysplasia is a painful and frequently disabling condition of instability between the acetabulum and the femoral head. It usually results from insufficient formation of the acetabulum, which is the cup-shaped socket that receives the femoral head. As the hip is a load-bearing joint, instability in the positional relationship of the acetabulum and the femoral head frequently results in further injury to surrounding tissue.
Surgical techniques for correcting hip dysplasia have been suggested, notably the pelvic osteotomy. In that procedure, an acetabular segment is rotated to allow the underformed acetabulum better to "cover" the femoral head. This is an invasive procedure requiring at least three pelvic incisions. Conventional fixation plates are incapable of withstanding the shear and torque forces incident to acetabular segment rotation, resulting in loss of fixation. Bowel and urinary tract complications frequently result from constriction of the pelvic canal. Worse, a pelvic osteotomy performed by a skilled surgeon often fails to correct the instability between the acetabulum and the femoral head. That is because rotation of the acetabular segment to "cover" the femoral head typically does little to compensate for the joint capsule stretched by the dysplastic process.
It has been discovered that merely lengthening the biomechanical femoral neck--referred to herein as the femoral neck--will, in many cases, correct hip dysplasia. When the femoral neck is lengthened, the femoral head may be fitted more deeply within the acetabulum (even an underformed one), thus stabilizing the joint without resort to a pelvic osteotomy. It has also been discovered that improved results may be obtained from a pelvic osteotomy, when performed in combination with a femoral neck-lengthening osteotomy. A relatively simple and less invasive femoral neck-lengthening osteotomy procedure would then obviate the pelvic osteotomy procedure in some cases, and complement it in others.
In a related syndrome, the proximal end of the femur is found to be rotated about the long axis with respect to the distal end. Successful stabilization of the coxofemoral joint depends upon properly aligning, as well as positioning, the acetabulum and the femoral head. A femoral neck-lengthening osteotomy procedure that allowed preferably concurrent lengthening of the femoral neck and resolving of this torsional deformation would then permit stabilization of the coxofemoral joint even in the case of the twisted femur.
Osteotomies have been used to correct a variety of bone malformations. Intentionally in some cases, and incidentally in others, performance of an osteotomy results in a discontinuity in the median axis of, for example, the tibia or femur. That is a frequently undesirable result, as it tends to weaken these load-bearing members. In order to maximize the post operative, load-bearing capacity of the affected member, a femoral neck-lengthening osteotomy procedure capable of preserving the continuity of the femur's median axis is desirable.
The present invention discloses a technique whereby the femoral neck may be lengthened and, optionally, torsed to relieve the condition of hip dysplasia. As used herein, the coined term "torse" derives from the noun torsion, and means to pivot, relative to the acetabulum, or to twist about the median femoral axis, relative to the distal end of the femur.
A principal object of the invention is to provide an osteotomy technique that lengthens the femoral neck to restore the proper positional relationship between the femoral head and the acetabulum.
Another important object of the invention is to provide an osteotomy technique that torses the femoral neck to restore the proper angular relationship among the femoral head, insertion of the internal and external rotator muscles of the hip and the acetabulum.
A further object of the invention is to provide a technique that accomplishes both the lengthening and torsing of the femoral neck in a single surgical procedure.
Still another object of the invention is to provide a technique that achieves these objects while maintaining the continuity of the femur's median axis.
According to a preferred method of practicing the invention, a cut is made in the proximal end of the femur. The cut is made generally parallel with the sagittal plane. The cut is positioned substantially to bisect the proximal end of the femur over a predetermined distance, creating two relatively movable femoral portions. The femoral portions are then diverged relative to one another by the desired corrective distance. Finally, the femoral portions are fixed in any suitable manner against further relative movement. The femoral neck is thereby lengthened to stabilize its load-bearing relationship with the acetabulum.
According to a modification of this preferred method of practicing the invention, a cut is made as described above, except that the cut is terminated at an angle in the plane of the cut. The modified cut thus extends farther in the cranial region of the femur than it does in the caudal region. While the thus-cut femoral portions are diverged, they are also rotated relative to one another through the desired corrective angle. Fixation is accomplished as described above. By this modified technique, the femoral neck is lengthened and also torsed to correct any femoral malformation and to ensure proper alignment of the femoral head and the acetabulum.
By either the preferred or modified method of practicing the invention, a single planar cut in the femur allows a range of divergence and relative rotation of the cut femoral portions to achieve the desired degree of lengthening and torsing of the femoral neck.
These and other advantages and features of the invention will become more fully apparent when the detailed description below is read with reference to the accompanying drawings.